1. Field of the Invention
The present invention relates to a wheel-speed abnormality detecting apparatus for detecting an abnormality in wheel-speed sensors and the like.
2. Related Background Art
A conventional wheel-speed abnormality detecting system is described in Japanese Patent Publication No. 2803472. This system is constructed to recognize that there is an abnormality in the wheel-speed sensors when a speed difference between the left and right non-driven wheels is over a predetermined value.
Under such circumstances that rotation of a specific wheel is physically restrained in comparison with rotation of the other wheels (e.g., when the specific wheel is in a stuck state), however, the speed difference between the left and right wheels becomes over the predetermined value, though the wheel speed sensor for the specific wheel is normal. The above conventional system thus misjudges that this state is an abnormality in the sensor accordingly.
The present invention has been accomplished in view of this problem and an object of the present invention is thus to provide a wheel-speed abnormality detecting apparatus restrained from making such a misjudgment.
In order to solve the above problem, the present invention presents a wheel-speed abnormality detecting apparatus for, with such detection that a wheel speed of at least one specific wheel is nearly equal to zero but wheel speeds of the other wheels are not nearly equal to zero, making a judgment that the wheel speed of the specific wheel is abnormal, wherein the abnormality judgment is canceled when rotation of the specific wheel is physically restrained in comparison with rotation of the other wheels.
In this case, when the rotation of the specific wheel is physically restrained in comparison with the rotation of the other wheels, the abnormality judgment is canceled even if the wheel speeds detected are in the above relation. Therefore, the apparatus is restrained from making a misjudgment.
The apparatus may also be arranged so that the above abnormality judgment is canceled by resetting a detection time necessary for the abnormality judgment.
Further, this wheel-speed abnormality detecting apparatus is preferably constructed so that a judgment that there is an abnormality in wheel speed is made when a predetermined relation is not established between an estimated wheel speed estimated based on speed of an engine for driving wheels and an average of wheel speeds of all the wheels.
The apparatus is characterized in that this predetermined relation is a relation of agreement or approximate agreement. The approximate agreement means agreement of these within xc2x120%.
It is preferable that all the wheels can be driving wheels under traction control.